Year	US Dollars adjusted for inflation)
1980	16.35
1981	16.96
1982	17.66
1983	18.46
1984	18.65
1985	18.98
1986	19.81
1987	20.41
1988	20.59
1989	20.55
1990	20.65
1991	21.18
1992	22.09
1993	23.01
1994	23.66
1995	24.01
1996	24.6
1997	24.96
1998	25.45
1999	25.91
2000	26.73
2001	27.07
2002	27.78
2003	28.57
2004	29.39
2005	29.72
2006	30.43